Aqueous dispersions of polyurethanes or polyurethane ureas are known (for example, in Angewandte Chemie, 82 (1970) pages 53 to 63 and U.S. Pat. Nos. 3,920,598 and 3,905,929). These dispersions are of high quality.
Not least among the factors which contribute to this high quality is the fact that many of these dispersions are free from emulsifiers. They contain chemically incorporated hydrophilic centers which make the otherwise hydrophobic elastomers self-emulsifiable. This method of making dispersions self-emulsifiable has two major advantages over the use of emulsifiers:
(1) a smaller number of hydrophilic centers is required; PA1 (2) the built-in emulsifier cannot migrate inside molded products produced from such elastomer dispersions; this generally has an important influence on the overall properties of the product. PA1 (a) polyalkylene oxide-polyether chains in terminal positions containing from 0.5 to 10%, by weight, of ethylene oxide units, based on the total quantity of polyurethane, and PA1 (b) a content of from 0.1 to 15 milliequivalents of .dbd.N.sym..dbd., --S.sym.--, --COO.crclbar. or --SO.sub.3 .crclbar. groups per 100 g. PA1 (a) an organic diisocyanate, PA1 (b) an organic compound which behaves as a difunctional material in the reaction with the diisocyanate and which contains isocyanate reactive hydrogen atoms, PA1 (c) a first hydrophilic material selected from the group consisting of PA1 (d) a second hydrophilic material selected from the group consisting of PA1 (1) dihydroxypolyesters generally known in polyurethane chemistry, which are obtained from dicarboxylic acids (such as succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid; terephthalic acid; tetrahydrophthalic acid; and the like) and diols (such as ethylene glycol; propylene glycol-(1,2); propylene glycol-(1,3); diethylene glycol; butanediol-(1,4); hexanediol-(1,6), octanediol-(1,8), neopentyl glycol; 2-methylpropanediol-(1,3); the various isomeric bis-hydroxymethyl cyclohexanes; and the like); PA1 (2) polylactones generally known from polyurethane chemistry, e.g., polymers of .epsilon.-caprolactone started on the above-mentioned dihydric alcohols; PA1 (3) polycarbonates generally known from polyurethane chemistry, obtainable by, for example, reaction of the above mentioned diols with diarylcarbonates or phosgene; PA1 (4) polyethers generally known in polyurethane chemistry; examples include the polymers or copolymers of styrene oxide, propylene oxide, tetrahydrofuran, butylene oxide or epichlorohydrin which may be prepared with the aid of divalent starter molecules such as water, the above-mentioned diols or amines containing two NH bonds; certain proportions of ethylene oxide may also be included, provided the polyether used does not contain more than about 10%, by weight, of ethylene oxide; however, polyethers obtained without the addition of ethylene oxide are generally used; PA1 (5) polythioethers, polythio mixed ethers and polythio ether esters generally known in polyurethane chemistry; PA1 (6) polyacetals generally known in polyurethane chemistry, for example, those obtained from the above-mentioned diols and formaldehyde; and PA1 (7) difunctional polyether esters containing isocyanate-reactive end groups generally known in the art. PA1 (a) any monoisocyanates and/or compounds which are monofunctional in the isocyanate polyaddition reaction and contain an isocyanate-reactive hydrogen atom, which monoisocyanates and compounds contain hydrophilic chains which have ethylene oxide units and PA1 (b) any mono-or di-isocyanates and/or compounds which are monofunctional or difunctional in the isocyanate polyaddition reaction and contain isocyanate-reactive hydrogen atoms, which mono- or di-isocyanates and compounds contain ionic groups or groups capable of conversion into ionic groups. PA1 R represents a divalent group obtainable by removal of the isocyanate groups from a diisocyanate represented by the formula R(NCO).sub.2 described above, PA1 R' represents a monovalent hydrocarbon group having from 1 to 12 carbon atoms, and preferably an unsubstituted alkyl group having from 1 to 4 carbon atoms, PA1 X represents the radical obtained by removal of the terminal oxygen atom from a polyalkylene oxide chain having from 5 to 90, and preferably from 20 to 70 chain members, of which at least 40%, and preferably at least 65%, are ethylene oxide units, while the remaining members may consist of other alkylene oxide units including propylene oxide, butylene oxide or styrene oxide units, preferably propylene oxide units, PA1 Y and Y' preferably represent oxygen but may also represent NR" in which R" has the meaning defined for R' or, in the case of Y', it may also represent hydrogen, PA1 Z represents a group having the meaning defined for Y. PA1 A and B represent an aliphatic hydrocarbon group having from 2 to 6 carbon atoms, and preferably an ethylene group, and PA1 cat.sym. represents a substituted or unsubstituted ammonium cation or, preferably, a sodium or potassium cation. PA1 U represents --O--CO--NH--, --NH--CO--NH--, --NH--CO-- or --S--CO--NH-- and PA1 R, X, Y, and R" have the meaning already indicated. PA1 (1) the number of non-ionic hydrophilic segments present, PA1 (2) the particle size of the disperse phase (determined by measuring the light scattering), and PA1 (3) the solids content of the dispersion.
In particular, the first of these two features considerably reduces the sensitivity to water of molded products produced from self-emulsified polyurethanes. The hydrophilic centers incorporated in these known water-dispersible polyurethanes or polyurethane ureas may be both salt-like, i.e., ionic groups, and also hydrophilic non-ionic groups. Among the last mentioned non-ionic polyurethanes which are dispersible in water may be included in particular the polyurethanes or polyurethane ureas containing polyethylene oxide units in side chains as described in U.S. Pat. Nos. 3,920,598 and 3,905,929.
The dispersions of these polyurethanes have a variety of characteristic properties depending on the type of hydrophilic center. Polyurethane ionomer dispersions, for example, are resistant to heat up to their boiling point because the solubility of the salt groups contained in them is virtually independent of the temperature, whereas non-ionic dispersions coagulate even when heated to moderate temperatures (e.g., about 60.degree. C.) because the polyethylene oxide side chains gradually lose their solubility in water at elevated temperatures. Unlike ionomers, these dispersions are unaffected by the addition of substantially unlimited quantities of electrolytes and are also resistant to freezing and thawing.
The sensitivity to electrolytes is particularly high in cationic polyurethanes. Aqueous dispersions of polyurethanes containing quaternary ammonium or tertiary sulphonium groups coagulate instantly even when only a very small quantity of an electrolyte having monovalent ions, such as sodium chloride, is added in aqueous solution. Due to this property, the preparation and application of cationic polyurethane dispersion involve special problems. The water used for their preparation must generally be substantially free from ions. So-called "hard" water causes undesirable coarsening of the dispersed particles or partial coagulation. Pigmentation of cationic dispersions is frequently difficult because ions adsorbed on the surface of the pigments obstruct incorporation of the pigments and lead to unsatisfactory results. The extreme sensitivity of cationic polyurethane dispersions to various additives has made their commercial application very difficult or even impossible. On the other hand, cationic dispersions have very desirable properties such as very firm adherence to a variety of substrates and excellent film-forming properties.
The present invention provides new water dispersible polyurethanes which, in the form of their aqueous dispersions, combine the advantages of excellent frost-resistance and resistance to electrolytes with the advantage of very high temperature resistance.